1. Field of the Invention
This invention pertains to wafer-scale integration (WSI) and, more particularly, to memory devices. It is specifically directed to a condensed memory matrix (CMM) having application to memory modules, memory cards, hard drives and the like.
2. State of the Art
Wafer-scale integration (WSI) refers generally to a method for maintaining functionally defined and independently testable "chips" (or dies) on a wafer. WSI has always been understood as a method of fabrication rather than a size of fabrication. Currently, while wafers are routinely constructed as discs up to nine (9) inches, more typically, wafers are produced being seven (7) inches in diameter, although the wafer size may vary as manufacturing capabilities vary. Conventionally, selected "good" chips are interconnected through wiring deposited on the wafer, rather than dicing the wafer and interconnecting individual chips by means of single chip packaging or other expedients. Portions of the disc, carrying a requisite number of dies, may be cut from the wafer for use in the construction of a device. The primary goal of WSI has been to increase system density beyond that achievable by maximizing chip size within an ordinary packaging environment. It is also generally understood that increasing density improves system performance and decreases system cost.
To realize increased density, good chip yield on the wafer must be very high. Otherwise, dilution of good chips with bad chips on the wafer will work against density gain. All of the chips on a wafer must ordinarily be fabricated from the same process for the wafer to be competitive, on either an economic or performance basis, with independently produced single chips. This is understood as meaning that all chips on a wafer must be of the same type (no mixing of DRAM, SRAM, Logic, EPROM, etc. on the same wafer). Wafers with only DRAM chips, especially DRAM chips of small size, find practical application in the construction of a memory.
U.S. Pat. No. 5,214,657 discloses a method for utilizing the good portions of an otherwise defective WSI wafer. Specifically, circuitry is provided to enable dicing of the wafer to salvage discrete memory sections should the wafer as a whole fail testing. Fuses in the wiring laid down on the wafer may selectively be blown to isolate defective dies from the circuits interconnecting the good dies.
Hybrid WSI (HWSI) has been suggested to avoid some of the practical limitations of WSI. HWSI involves mounting tested good chips of any type on a tested good wafer. The wafer provides passive chip interconnections, power distribution and intermediate cooling. The HWSI approach forgoes the economical benefits of conventional WSI and has the disadvantage of making cooling more difficult since the glue required to bond the chips to the wafer causes an additional temperature drop in the cooling path.
There remains a need in the art for further refinements in WSI technology whereby a wafer or a portion of a wafer may be connected to a substrate material, such as a substrate circuit board (SCB). Such a construction would increase system density in a memory device, and would provide practical portability for such devices at low cost.